The present invention relates generally to an electronic waveform display system, and more particularly to one having a secondary or readout display function.
The readout provides an alphanumeric display to provide an operator with various information such as parameter settings, operation status, measurement results, etc. using LED, LCD devices or a cathode ray tube (CRT) in an electronic waveform display system such as an oscilloscope.
The present invention is directed to an improvement of the type wherein a CRT is commonly used for the secondary or readout display along with waveform display. In such a waveform display system, the readout is usually displayed on upper and lower portions of the CRT screen in order to not disturb the displayed waveforms. Also, an electron beam of the CRT is used for both waveform and readout display in a time sharing manner.
Ideally, readout information should be displayed only when the system is not displaying waveform traces, in order not to interfere with the waveform display. The readout occurs before a trace commences, after a trace is completed, or between consecutive traces. Refreshing the readout within such periods causes no interference with the displayed waveforms.
However, such a technique is not effective over the entire sweep rate range of the waveform. Flicker of the readout display occurs at lower sweep rates. Also, the period between the consecutive traces may be insufficient to finish the readout display at very high sweep rates. Accordingly, momentary interruptions of the waveform are needed at such sweep rates to maintain the readout display flicker-free and at a constant intensity. As a result, intensity modulation of the waveform display is apparent at moderate sweep rates, caused by closely spaced, individually imperceptible interruptions.